1. Field of the Invention
The present invention relates to a control process for a matrix screen having two independent parts and an apparatus for performing the sane. It more particularly applies to all matrix screens controlled in two independent parts and in particular to video screens (e.g. liquid crystal screens or microdot fluorescent screens).
2. Brief Description of Prior Art
With reference to FIG. 1 a description is given of a prior art matrix screen of this type. Such a screen is constituted by a first part 10 and a second part 12, which are independent bat contiguous. Each part 10, 12 of the screen has N control rows intersecting M addressing columns. For the display, the rows of the first part 10 are successively selected simultaneously with the rows of the second part 12, i.e. row 1 of the first part 10 with row N+1 of the second part 12, row 2 with row N+2 and so on.
The rows are selected by a first register 6 for the first part 10 and a second register 8 for the second part 12. Signals DP for the register 6 and DS for the register 8 supply the data relating to the row to be selected. A row scanning signal HL controls the row selection.
The registers 6 and 8 are respectively connected to amplifying and impedance adapting means 9 and 11 making it possible to apply a given potential to the selected rows.
For each selection of a row of one part simultaneously with a row of the other part, the informations to be displayed are contained in binary coded form in a first and a second registers 14, 16 permitting the addressing of the columns. The first and second registers 14, 16 are connected to decoders 21, 23 permitting the application to the screen columns of potentials corresponding to the informations to be displayed on the pixels of the selected rows. For the duration of said selection, the informations to be displayed during the following selection are recorded in a first end a second buffer registers 18, 20, which are respectively connected to the first and second registers 14, 16 for the transfer of the informations to be displayed.
For a video type signal V supplied by a source 22, the informations to be displayed are supplied in series row by row. Therefore an intermediate memory 24 is required and at a given instant the informations supplied only relate to a single row, whereas two rows are simultaneously displayed and it is also necessary to fill the two buffer registers 18, 20.
Therefore the said memory 24 records the informations to be displayed during their arrival and supplies the buffer registers 18, 20 with the informations necessary for the display. For this purpose it must be able to record the informations to be displayed on all the rows of each screen part 10, 12. It mast therefore have a minimum capacity of 2N M K bits in which 2N is the number of screen rows, M the number of columns and K the number of bits necessary for coding the informations to be displayed on one pixel.
The large capacity of the memory is a serious disadvantage of this known screen, the apparatus costs increasing with the size of the same.